Linking mercury exposure to habitat and feeding behaviour in Beaufort Sea beluga whales

Mercury (Hg) levels in the Beaufort Sea beluga population have been increasing since the 1990's. Ultimately, it is the Hg content of prey that determines beluga Hg levels. However, the Beaufort Sea beluga diet is not understood, and little is known about the diet Hg sources in their summer habitat. During the summer, they segregate into social groups based on habitat use leading to the hypothesis that they may feed in different food webs explaining Hg dietary sources. Methyl mercury (MeHg) and total mercury (THg) levels were measured in the estuarine-shelf, Amundsen Gulf and epibenthic food webs in the western Canadian Arctic collected during the Canadian Arctic Shelf Exchange Study (CASES) to assess their dietary Hg contribution. To our knowledge, this is the first study to report MeHg levels in estuarine fish and epibenthic invertebrates from the Arctic Ocean. Although the Mackenzie River is a large source of Hg, the estuarine-shelf prey items had the lowest MeHg levels, ranging from 0.1 to 0.27 μg/g dry weight (dw) in arctic cisco (Coregonus autumnalis) and saffron cod (Eleginus gracilis) respectively. Highest MeHg levels occurred in fourhorn sculpin (Myoxocephalus quadricornis) (0.5 μg/g dw) from the epibenthic food web. Beluga hypothesized to feed in the epibenthic and Amundsen Gulf food webs had the highest Hg levels matching with high Hg levels in associated food webs, and estuarine-shelf belugas had the lowest Hg levels (2.6 μg/g dw), corresponding with the low food web Hg levels, supporting the variation in dietary Hg uptake. The trophic level transfer of Hg was similar among the food webs, highlighting the importance of Hg sources at the bottom of the food web as well as food web length. We propose that future biomagnification studies incorporate predator behaviour with food web structure to assist in the evaluation of dietary Hg sources.     

Structural changes in commuting in the Toronto region 1971–1981

Changes in the commuting structure of the Toronto CMA are examined using 1971 and 1981 census journey to work data. There have been important changes in household structure, the employment base and the associated location decisions which in turn have created significant changes in commuting structure. The proportions of one‐ and two‐person households increased sharply over the decade and many of these smaller‐sized, high occupational status households were located in the older inner residential areas. The bulk of the larger‐sized households continued to be located on the developing fringe where housing prices are much lower. The structure of the employment base shifted over the decade with a reduction in the proportion of manufacturing jobs and growths in the proportions of jobs in finance and services, with the bulk of these office‐based jobs located in the Yonge Street transit corridor. Job growth in the suburbs was dominated by employment in manufacturing, transportation, trade and services. The addition of some 100000 jobs in the Yonge Street corridor resulted in strong commuting growth from the inner suburbs as well as from the newly developing outer suburbs. About half of the labour force living in the outer suburbs in the decade found local jobs, with the remainder of the labour force commuting to jobs in Metropolitan Toronto, principally along the high‐mobility transit and freeway corridors.     

Performance ranking methodology for roading operations management

Management of enterprises in the public domain are being asked to look beyond financial measures of performance towards a system of performance indicators which will reflect achievement in quantitative but not necessarily monetary terms. The essential element of this approach is the role that management must play in the selection of indicators which reflect key dimensions of performance and objectives of the organization. This paper identifies comparison and presentation methods which are likely to be of practical help to managers facing the tasks of control and communication in the wider accountability process.

The issues raised are illustrated in a case study derived from an analysis of road maintenance management data from New Zealand territorial local authorities 1982–87.     

A systems approach to area traffic control

Since the first pilot scheme for area‐traffic control was introduced in the city of Montreal (1959–60), computer control of traffic in urban areas through the adaptation of existing traffic‐signal systems has been provided to an increasing extent. This area of work may pose problems for the professional traffic engineer whose background in computer technology and general digital electronics may be limited.

In considering the engineering implications of such schemes a systems approach is important and is adopted here. Three existing and representative schemes are briefly mentioned in order to outline basic features. A more detailed examination of the various system elements follows with mention of data collection and transmission, and the role of the control computer.

The paper continues with a reconsideration of the three representative schemes in the light of the detailed treatment of system components. It concludes with a tentative assessment of the present position of area traffic control schemes and some suggestions as to the future development.     

Experimental investigation of the strength and stability of submarine pressure hulls with and without artificial corrosion damage

A submarine may have to operate for a period of time with local corrosion damage in the pressure hull if a suitable repair method is unavailable or too expensive for implementation. This paper describes collapse tests on twenty ring-stiffened aluminium cylinders, which were conducted to study the effect of corrosion damage on hull strength and stability. Artificial hull thinning was found to reduce the collapse strength of experimental models through high local stresses in the corroded region, leading to early onset of yielding and inelastic buckling. Bending associated with the eccentricity due to one-sided thinning was found to further increase the local stresses in the hull. Overall collapse pressures were more severely affected by corrosion damage than interframe collapse pressures. The percentage reduction in overall collapse pressure, compared with intact experimental models, was found to be closely related to the percentage depth of thinning. The accuracy of conventional collapse pressure predictions for the experimental models was significantly better for intact than for corroded cylinders.     

Modeling Potential Impacts of Beach Replenishment on Horseshoe Crab Nesting Habitat Suitability

Beach replenishment has been proposed to increase nesting habitat for horseshoe crabs, but its environmental consequences may compromise the egg development and viability of this declining species. Horseshoe crab habitat requirements were used to build a habitat suitability model in STELLA to predict the potential impacts of beach replenishment on horseshoe crab eggs. A habitat suitability index (H.S.I.) comprised of six variables (dissolved oxygen, sediment grain size, sand temperature, sand moisture, wave energy, and salinity) was developed and compared between replenished and natural beaches. Sediment grain size and dissolved oxygen were higher in the natural beach, whereas sand temperature and moisture were higher in the replenished beach, resulting in significantly higher suitability of the natural beach (p = 5.39 × 10^?15, df = 30). The model was most sensitive to air temperature, rainfall, tide, and sediment grain size. This model is useful for understanding the processes affecting horseshoe crabs and predicting impacts of coastal management activities on habitat suitability. Based on the results of this model, beach replenishment is not recommended for increasing or improving horseshoe crab habitat, unless care is taken to match fill sediment to natural grain size and color.     

Book Review

Vehicle Replacement — A Management Guide. By John E. Sussams. (Gower, 1983.) [Pp. 102.] £19.50.     

It's a Wonderful Coast or,Every Time a Bell Rings,Long Island Sound is Protected

In Frank Capra's classic film It's a Wonderful Life, a despondent man takes a journey to see what life would have been like without him: the journey paints a bleak picture. In true Hollywood form, he is ultimately reassured of his impact even though his accomplishments were immeasurable. The film's protagonist, George Bailey, is the perfect metaphor for Connecticut's Coastal Management Program. The Program can measure quantifiable elements: the number of site plans reviewed, number of permits issued, acres of tidal wetlands restored. But coastal managers often lose sight of the accomplishments and ripple effects of management, possibly because accomplishments are taken for granted. Perhaps the true value of coastal management programs lies in that intangible, immeasurable idea of what coasts would be like without them.

This article takes readers on a George Bailey–esque journey by identifying the Connecticut Coastal Management Program's accomplishments since its adoption in 1980, reviewed in the context of several questions: What if the Program had never been adopted? What would public access look like? How many acres of tidal wetlands would be lost to development or Phragmites invasion? Hopefully, the results of the exercise will put coastal management into better context and highlight the successes.     

Stochastic optimization in cooperative relay networks for revenue maximization

In cellular networks, cooperative relaying is an economic and promising way to enlarge the network capacity and coverage. In the case that multiple users and multiple relays are taken into account, efficient resource allocation is important in such networks. In this paper, we consider the joint relay power control with amplify- and-forward （AF） strategy and dynamic pricing for uplink cellular networks in order to maximize the network administrator＇s system revenue. The system revenue is associated with pricing strategies and mobile users＇ random data request, which is supported by the relay assisted transmission. To deal with the problem of the coupling in pricing and relay resource allocation, we utilize Lyapunov optimization techniques to design online pricing and relay power control without any statistic information of random events in networks. Theoretical analysis shows that the proposed algorithm can achieve a near-optimal performance and simulation results also validate its effectiveness and robustness.